1. Field of the Invention
This invention relates to a digital signal processing device and method for recording or transmitting compressed data produced on bit compression of digital audio signals or the like, and a recording medium having recorded thereon the compressed data produced by the digital signal processing method. More particularly, it relates to a digital signal processing method and device for handling digital audio signals including high tonality signals, and a recording medium.
2. Description of the Related Art
The present Assignee has already proposed in U.S. patent application Ser. No. 08/171,283 now U.S. Pat. No. 5,521,900, issued on May 28, 1996, JP Patent Kokai JP-A-4-105270, U.S. Pat. No. 5,243,588 and in U.S. Pat. No. 5,244,705 a technique of bit-compressing input digital audio signals and recording the bit-compressed signals on a recording medium in a burst fashion with a pre-set data quantity as a recording unit.
In the U.S. Pat. No. 5,521,900, there is described a disc recording device comprised of a disc having data indicating the recording contents in a data region as main data in a lead-in region having sub-coded table-of-contents data indicating the recording position of the data region recorded thereon, and means for recording data on the disc. There is also disclosed a disc reproducing apparatus comprised of means for reproducing data on the disc and means for making display corresponding to the display data produced by the reproducing means. In the JP Patent Kokai JP-A-4-105270, there is disclosed a disc recording device which is comprised of memory means on which continuous input data is sequentially written and from which the input data written thereon is sequentially read out as recording data at a readout rate faster than the transfer rate for input data, driving means for rotationally driving the disc-shaped recording medium at a commutable rate, means for recording data read out from the memory means on the disc-shaped recording medium, memory control means for sequentially reading the input data recorded in the memory means in a pre-set quantity when the input data quantity recorded on the memory means exceeds a predetermined quantity for maintaining a writing space in the memory means in more than a pre-set data quantity, and recording control means for controlling the recording position for continuously recording the recording data sequentially discontinuously read out from the memory means on the recording tracks on the disc-shaped recording medium under control by the memory control means. There is also disclosed a corresponding device for reproducing data recorded on the disc-shaped recording medium. In the U.S. Pat. No. 5,243,588, there is disclosed a disc recording device having memory means for transiently storing digital data and recording means for recording digital data from the memory means on a disc-shaped recording medium by clustering the digital data from the memory means at an interval of a pre-set number of sectors, providing a cluster-linking sector having a length longer than the interleaving length at each connecting portion of the clusters, and interleaving the digital data. There is also disclosed a corresponding device for reproducing data recorded on the disc-shaped recording medium. In the U.S. Pat. No. 5,244,705, there is described a disc-shaped recording medium having compresses audio data etc., recorded thereon, in which, if the inner diameter of the recording region of the disc-shaped recording medium is in a pre-set range of from 32 to 50 mm, the outer diameter of the recording region is set to 60 to 62 mm and to 71 to 73 mm for the inner diameter of the disc recording region of 32 mm and 50 mm, respectively, whereby the recording medium may be used for a small-sized portable disc recording/reproducing device and whereby the reproducing time on the order of that of a standard 12 cm CD may be achieved by recording compressed audio data at a compression ratio of 1/4.
With such technique, a magneto-optical disc is used as a recording medium, and adaptive differential (AD) PCM audio data, as prescribed in an audio data format of so-called CD-I (CD-Interactive) or a CD-ROM XA, is recorded and reproduced. The ADPCM audio data is recorded on the magneto-optical disc in a burst fashion using e.g., 32 sectors of the ADPCM audio data and several linking sectors for an interleaving operation as a recording unit.
Several modes may be selected with the ADPCM audio data in the recording/reproducing device employing the magneto-optical disc. For example, there are prescribed a mode having a level A having a sampling frequency of 37.8 kHz with a compression ratio which is twice as compared with the reproducing time of a conventional compact disc (CD), a mode having a level B having a sampling frequency of 37.8 kHz with a compression ratio which is four times as compared with the reproducing time of the compact disc and a mode having a level C having a sampling frequency of 18.9 kHz with a compression ratio which is eight times as compared with the reproducing time of the compact disc.
That is, with the above level B, the digital audio data are compressed to approximately 1/4, such that the play time of the disc recorded with the level B mode is four times that of the standard CD format (CD-DA format). Since the recording/reproducing time may be on the same order as that of a small sized disc having a standard diameter of 12 cm, the recording/reproducing device may be reduced in size.
However, with the recording/reproducing device employing the magneto-optical disc, since the rotational speed of the disc is the same as that of a standard CD, the amount of the compressed data obtained with the level B per pre-set time is four times that of the standard CD. Consequently, the same compressed data is read in superimposition four times, in a time unit of e.g., a sector or a cluster, and only one of the four superimposed compressed data is transmitted to audio reproduction. Specifically, during scanning or tracking a spiral recording track, track jump of returning the optical pickup to the starting track position is performed for each revolution for repeatedly tracing the same track four times on end by way of reproduction. This indicates that at least one sound compressed data of the four superposed reading operations suffices and hence the disclosed technique is strong against errors otherwise caused by disturbances and consequently may be desirably applied above all to a small-sized portable type device.
Besides, a semiconductor memory is scheduled to be employed in future as a recording medium. For further improving the compression efficiency, it is desirable to achieve further bit compression. Specifically, audio signals are recorded and/or reproduced using a so-called IC card, on or from which bit-compressed data is recorded or reproduced, respectively.
With the IC card, employing the semiconductor memory, the increase in the storage capacity or low costs are achieved with the progress in the semiconductor technology. Notwithstanding, at an earlier stage when the IC card has started to be supplied to the market, it is thought to be short of the storage capacity and expensive. Therefore, it may be contemplated to transfer the recording contents of an inexpensive large-capacity recording medium, such as the magneto-optical disc, to the IC card by way of performing frequent re-writing operations. Specifically, desired ones of musical numbers recorded on the magneto-optical disc are dubbed to the IC card and exchanged with other musical numbers in a desired manner. By frequently re-writing the contents of the IC card in this manner, performance of a wide variety of musical numbers may be enjoyed outdoors with a small number of IC cards on hand.
The present Assignee has already proposed in our European Patent Application (Publication Number: 0525809 A2; date of publication, 03 02 93) an encoding method suitable for generating the above-mentioned compressed data.
The present Assignee has also proposed in our European Patent Application (Publication Number: 0599719 A1; date of publication, 01 06 94), European Patent Application (Publication Number: 0601566 A1; date of publication, 15 06 94) and in our International Publication Number: WO 94/19801 (International Publication Date: 1 Sep. 1994) a recording/reproducing system suitable for recording/reproduction, in which the above-mentioned IC card is utilized.
If, with a view to prolonging the recording time, the bit rate for high efficiency encoding is lowered, deterioration in the sound quality becomes gradually outstanding, as is most pronounced with music signals wherein acoustic effects are critical.